Conventional acceleration sensors generally have an oscillating structure as a seismic mass suspended movably on a substrate. This seismic mass is deflected by an acceleration acting on it and changes its position relative to the substrate. Analyzing means are provided for the seismic mass to detect the degree of deflection due to acceleration. Known analyzing means include piezoresistive, capacitive and frequency-analog analyzing arrangements, for example. With capacitive analyzing means, the seismic mass is provided with a comb structure that works together with a stationary (i.e., attached to the substrate) comb structure. Capacitances that vary in size with deflection of the seismic mass develop between the individual webs of the comb structures. These changes in capacitance can be detected by analyzing circuits, and thus an acceleration acting on the acceleration sensor can be detected.
One disadvantage of the known acceleration sensors is that there may be fluctuations in the length of the substrate or the sensor structures depending on temperature or mechanical stresses, for example, causing minor variations in the positions of the seismic mass suspended on the substrate or in the analyzing means, subsequently causing a change in the signal. These signal changes lead to faulty detection of an acting acceleration or they are superimposed on a signal of the analyzing means which is proportional to an acting acceleration with an offset error.
The acceleration sensor according to the present invention is advantageous in that fluctuations dependent on temperature or mechanical stresses occurring in the substrate or sensor structures can be compensated. Due to the fact that the oscillating structure and/or analyzing arrangement are connected to the substrate by mechanical decoupling devices, it is advantageously possible to compensate for any material effects in the substrate or sensor structures caused by compression and/or tensile stresses as well as fluctuations in temperature, so that they have no effect on the acceleration sensor, in particular its sensitivity. In addition, differences in material between the substrate and the sensor can be compensated with the mechanical decoupling devices, e.g. with acceleration sensors applied to a wafer by additive methods of surface micromechanics. Thus, for example, differences in the thermal expansion properties of silicon and metallic materials such as those used in some additive techniques can be compensated.